It is known that compatibility and adhesion between copolyether ester (TEEE) and polyamide (PA) is low.
Good adhesion between TEEE and PA would be desirable for co-extrusion, over-moulding and assembly by welding methods.
As a first example, plastic tubings prepared from polyamide resin are known and are used for various applications. However, single-layer polyamide tubings are not always capable of meeting all the requirements of chemical compatibility with the material flowing in them and resistance to the range of end-use temperatures and mechanical stresses. In particular, during transportation of aliphatic or aromatic solvents or fuels, they exhibit several problems, such as a lack of barrier action against the medium, dimensional instability and insufficient resistance to mechanical stresses.
Attempts have been made to solve these problems by the use of multilayer pipes comprising inner layers and/or barrier layers made of fluoropolymer (U.S. Pat. No. 5,743,304; WO 9744186; WO9409303), polyolefin (DE 3,715,251; DE 3,821,723), polyvinylalcohol (DE 3,510,395; DE 3,827,092) or combinations of these (DE 4,001,125; DE 4,001,126). Although these methods are useful for some applications, there is a need for alternatives providing a different combination of chemical resistance, temperature range, gas permeability and cost. For such co-extrusion applications, it is a further advantage to have a close match of the viscosity of the materials at processing temperature.
As a second example, both polyamides and copolyether esters have, for many years, been commonly used to form articles of all sizes and shapes. Each group of materials has its own advantages and drawbacks. More specifically, polyamides generally yield products having high rigidity and good resistance to many corrosive chemicals. In contrast, copolyester elastomers are renowned for their flexibility, resistance to fatigue, resistance to oils and hydrocarbons and soft touch characteristics. Since there are many mechanical and electrical components which comprise pluralities of functional parts, it is not surprising to note that in many cases, a combination of flexible and rigid materials is required.
Mechanical assembly methods (screw connections, snap-fitting) and adhesive joining are possible for dissimilar and incompatible materials, but they are not always acceptable for cost or performance reasons. Possible alternatives are the direct welding of separately molded parts and the special injection-molding methods like co-injection or multiple-shot molding. These methods require that the materials have a good adhesion to each other, otherwise the joining interfaces are not tight to either liquids or gases and can be separated with little force.
U.S. Pat. No. 5,149,589 recognises the problems of fusion bonding of synthetic resins such as polyamide to thermoplastic elastomers, particulary those having high rubber elasticity, namely the strength and sealing at the bond are unsatisfactory. It proposes therefore a composition of the thermoplastic elastomer with a thermoplastic polyester elastomer (TEEE) in given proportions, fusion bonded to the synthetic resin. However, such compositions have properties which are not suitable for all applications. In particular, the compositions including thermoplastic polyurethane (TPU) should not be processed at temperatures above 230.degree. C. because of the risk of decomposition to isocyanates, which limits their use in coextrusion applications. Also, these compositions have a high fraction of thermoplastic elastomer, so that they are too soft and rubbery for some mechanical requirements.
U.S. Pat. No. 4,268,570 recognises the problems of adhering polyester block copolymers to metal and discloses a metal-coated plastic product which comprises a molded mixture of a polyester block copolymer with a copolymer comprising an acrylic monomer, butadiene and styrene, and a metallic coating, optionally with an adhesive therebetween.